1. Field of the Invention
The present invention relates generally to motor decoding circuits and more particularly to a simplified three phase fullwave decoding circuit for DC motor commutation.
2. Description of the Prior Art
A large number of DC motor control and commutation systems are known at the present time. For example, attention is directed to U.S. Pat. Nos. 3,585,474 (Kobayashi, et al.), 3,590,353 (Kobayashi et al.) and 3,735,216 (Uemura), all of which disclose a first general type of known motor control systems. In particular, these references disclose half-wave commutation systems which inherently do not require decoding, but are lacking in certain performance characteristics. More specifically, such half-wave commutation systems are ordinarily characterized by a large torque ripple and a relatively low power efficiency. Thus, while these systems are quite simple and require a minimum of circuitry, their performance particularly at low speeds is often inadequate for devices such as magnetic tape drives, servo motors and the like, which require smooth and uniform output characteristics over wide speed ranges.
Other motor control devices having a 180.degree. ON time are also known, as disclosed for example in U.S. Pat. Nos. 3,720,856 (Bregeault) and 3,746,941 (Ageev et al.). Although these devices have improved torque characteristics relative to the half-wave commutation systems described above, they still experience a significant torque ripple particularly at low speeds, and are relatively inefficient in terms of power consumption.
A further category of motor control circuits is known in which torque and power characteristics are significantly improved relative to the two types of devices described above. However, these devices have generally required complicated logic switching networks to provide driving signals of the proper phase relationship and duration to provide the desired smooth torque performance over a wide range and the desired high power efficiency. Unfortunately, the complicated circuitry required by these systems has rendered them subject to failure due to the large number of components required, and has rendered them undesirably expensive for use in all but the most sophisticated type of systems.
Accordingly, a need exists for an improved three phase, full-wave DC motor decoding circuit of simple design which provides maximum performance in terms of smooth motor torque and power efficiency.